1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to transmitting and receiving uncompressed audio or video (AV) data, and more particularly, to transmitting and receiving uncompressed AV data over a wireless network by applying a different coding rate to each bit or each group of bits included in the uncompressed AV data according to the significance of each bit or each group of bits.
2. Description of the Related Art
As networks become wireless and the demand for large multimedia data transmission increases, there is a need for studies on an effective transmission method in a wireless network environment. In particular, the need for various home devices to wirelessly transmit high-quality videos, such as digital video disk (DVD) images or high definition television (HDTV) images, is growing.
An IEEE 802.15.3c task group is developing a technological standard for transmitting large-volume data over a wireless home network. The technological standard, which is called “millimeter wave (mmWave),” uses an electric wave having a physical wavelength of a millimeter (i.e., an electric wave having a frequency band of 30-300 GHz) to transmit large-volume data. This frequency band, which is an unlicensed band, has conventionally been used by communication service providers or used for limited purposes, such as observing electric waves or preventing vehicle collision.
FIG. 1 is a diagram which compares frequency bands of IEEE 802.11 series of standards and mmWave. Referring to FIG. 1, an IEEE 802.11b or IEEE 802.11g standard uses a carrier frequency of 2.4 GHz and has a channel bandwidth of approximately 20 MHz. In addition, an IEEE 802.11a or IEEE 802.11n standard uses a carrier frequency of 5 GHz and has a channel bandwidth of approximately 20 MHz. On the other hand, mmWave uses a carrier frequency of 60 GHz and has a channel bandwidth of approximately 0.5-2.5 GHz. Therefore, it can be understood that mmWave has a far greater carrier frequency and channel bandwidth than the related art IEEE 802.11 series of standards. When a high-frequency signal (a millimeter wave) having a millimeter wavelength is used, a very high transmission rate of several Gbps can be achieved. Since the size of an antenna can also be reduced to less than 1.5 mm, a single chip which includes the antenna can be implemented. Furthermore, interference between devices can be reduced due to a very high attenuation ratio of the high-frequency signal in the air.
A method of transmitting uncompressed audio or video data (hereinafter, referred to as uncompressed AV data) between wireless devices using a high bandwidth of a millimeter wave has recently been studied. Compressed AV data is generated after lossy compression processes which includes motion compensation, discrete cosine transform (DCT), quantization, and variable length coding (VLC) processes. In so doing, portions of the compressed AV data, to which human visual and auditory senses are less sensitive, are removed. On the other hand, uncompressed AV data includes digital values indicating pixel components (for example, red (R), green (G) and blue (B) components).
Hence, bits included in the uncompressed AV data have different degrees of significance while there is no difference in the significance of bits included in the compressed AV data. For example, referring to FIG. 2, a pixel component of an eight-bit image is represented by eight bits. Of the eight bits, a bit representing the highest order (the highest-level bit) is the most significant bit (MSB), and a bit representing the lowest order (the lowest-level bit) is the least significant bit (LSB). In other words, each of eight bits that form one byte of data has a different significance in restoring an image or audio signal.
An error that occurs in a bit of high significance during data transmission can be more easily detected than an error that occurs in a bit of low significance. Therefore, bit data of high significance needs to be better protected against errors that occur during wireless transmission than bit data of low significance. However, an error correction method, in which the same coding rate is applied to all bits that are to be transmitted as in the related art transmission method used by the IEEE 802.11 series of standards, has been used.
FIG. 3 is a diagram illustrating the structure of a physical layer (PHY) protocol data unit (PPDU) 30 of the IEEE 802.11a standard. Referring to FIG. 3, the PPDU 30 includes a preamble, a signal field, and a data field. The preamble, which is a signal for PHY layer synchronization and channel estimation, includes a plurality of short training signals and a long training signal. The signal field includes a RATE field indicating a transmission rate and a LENGTH field indicating the length of the PPDU 30. Generally, the signal field is encoded by a symbol. The data field includes a physical layer service data unit (PSDU), a tail bit, and a pad bit. Data to be transmitted is included in the PSDU.
Data recorded in the PSDU is composed of codes that are encoded using a convolution encoder. Bits that form data, such as compressed AV data, are not different in terms of significance. In addition, since the bits are encoded using the same error correction encoding method, an equal error correction capability is applied to each bit.
This related art data transmission method can be effective for general data transmission. However, if each portion of data to be transmitted has a different significance, it is required to perform more superior error correction encoding on portions of greater significance in order to reduce the probability of error occurrence.
In order to prevent error occurrence, a transmitting end performs error correction encoding on data. Even if an error occurs while the error-correction encoded data is transmitted, the error-correction encoded data can be restored as long as the error is within a correctable range. There are a variety of error correction encoding algorithms, and each error correction encoding algorithm has a different error correction capability. Even the same error correction encoding algorithm may show different performances depending on a coding rate used.
In general, as the coding rate increases, data transmission efficiency is enhanced, but error correction capability is reduced. Conversely, as the coding rate decreases, data transmission efficiency is reduced, but error correction capability is enhanced. As described above, since uncompressed AV data includes bits having different degrees of significance unlike compressed AV data, upper bits, which are more significant than lower bits, need to be better protected against errors during data transmission.
Related art methods of guaranteeing stable wireless data transmission include a method of restoring data using error correction encoding and a method of re-transmitting data having an error from a transmitting end to a receiving end. In particular, the present invention relates to a method of applying differential error correction encoding to bits that form uncompressed AV data according to the significance of the bits.